Hallo guy's need some help please. I have started the Quasi up without big problems. The green led's polarity were reversed. PCB silk from Thiago must be corrected. After that the Dc offset is OK and wanders a bit with +- 12mV. Bias is stable on 34mV . I however have some oscillation.When I switch the power off then the sine looks fine before the caps have completely discharged.(Third photo)
Running on +-40 rails.I have attached 33p in C8, does not make a big differance.
Q1-2n5401, Q2-2sc1845, Q3-2sa1381, Q4-bd139, Q5-2sa1381, Q6-irfp250, Q7-mjl3281.
Any ideas where to improve on this problem?🙂
Running on +-40 rails.I have attached 33p in C8, does not make a big differance.
Q1-2n5401, Q2-2sc1845, Q3-2sa1381, Q4-bd139, Q5-2sa1381, Q6-irfp250, Q7-mjl3281.
Any ideas where to improve on this problem?🙂
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Also, I have 100nf in C2 which must be 220pf. That can be a problem. I also don't have R4-22k resistor in parralel with C2. Some of Thiago's layouts have the R4 in and some don't. ?
Dont worry abt R4 and C2, for R4, put something like 33k, 47k, etc presently. In my sch, I have it at 47k. target / analyze your active devices, have you measured them?.
Sorry my fault, C2 is 220pf. Prasi I cannot find R4 on the schematic that Hugh has posted with working values ? There are also differences with resistor values.
R7-1k should be 680R, R9-1k should be 1K8,R8-47R should be 68R,R10-100k should be 68K, R19-100R should be 120R and feedback cap 470 should be 1000uf. The active devices are new from RS.Also the 2 input caps in series 47uf? That gives you 23uf for input cap ?
R7-1k should be 680R, R9-1k should be 1K8,R8-47R should be 68R,R10-100k should be 68K, R19-100R should be 120R and feedback cap 470 should be 1000uf. The active devices are new from RS.Also the 2 input caps in series 47uf? That gives you 23uf for input cap ?
Try a 2.2nF cap across the base/emitter of the npn quasi transistor.
The OnSemi device MJL3281 and the MJL4281 are very fast and require a little damping.
No other changes from DACZ schem are needed, should be fine.
Hugh
The OnSemi device MJL3281 and the MJL4281 are very fast and require a little damping.
No other changes from DACZ schem are needed, should be fine.
Hugh
Thanks Hugh, I'll try that. Should I leave C8 open ? Do I check Bias over R20 or R21 ? The Transitor bias is a little lower that over the Fet resistor.
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Guy's,still no pleasure. I have added the R//L output coil as well. No change. Inserted 2.2nf and also tried 10nf. Maybe I must try to replace the 2sc1845 with 2n5551 or replace ksa1381 with mje350? Any help plse.🙂
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Vrystaat,
I made a mistake; my apologies.
The 2.2nF should be across COLLECTOR/BASE, not emitter/base.
Don't bother with C8 just yet.
Hugh
I made a mistake; my apologies.
The 2.2nF should be across COLLECTOR/BASE, not emitter/base.
Don't bother with C8 just yet.
Hugh
That looks fine, Jan.
I would move on, check the offset, and start listening.
I think your amp is up and running now...... remember that there are artefacts in a square wave that are 11 times the fundamental, and moving very quickly at the transitions on a square wave can cause some overshot. That is normal; but music is NOT a square wave and this amp will be plenty fast.
Cheers,
Hugh
I would move on, check the offset, and start listening.
I think your amp is up and running now...... remember that there are artefacts in a square wave that are 11 times the fundamental, and moving very quickly at the transitions on a square wave can cause some overshot. That is normal; but music is NOT a square wave and this amp will be plenty fast.
Cheers,
Hugh
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And so it is. This amp sounds superbbbb ! As you say, it has a very sweet sound and nothing is missing or lacking. I am going to build the second channel and box it. Thanks to Ranchu, Hugh and everyone that were involved to make this happen !😀
Congratulations on a successful build Vrystaat! Happy listening!
Cheers,
X
When one knows that a second channel needs to built along with a proper case, we know we have a great amp.
Cheers,
X
When one knows that a second channel needs to built along with a proper case, we know we have a great amp.
The dc offset wanders a little between -12 and + 12 mv but I don't think that is bad. Bias very solid at 36mv. I'm happy !🙂
